CN110501738B - PET device and method for acquiring gamma ray generation position of scattered coincidence count in PET device - Google Patents
PET device and method for acquiring gamma ray generation position of scattered coincidence count in PET device Download PDFInfo
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- CN110501738B CN110501738B CN201910406803.XA CN201910406803A CN110501738B CN 110501738 B CN110501738 B CN 110501738B CN 201910406803 A CN201910406803 A CN 201910406803A CN 110501738 B CN110501738 B CN 110501738B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/29—Measurement performed on radiation beams, e.g. position or section of the beam; Measurement of spatial distribution of radiation
- G01T1/2914—Measurement of spatial distribution of radiation
- G01T1/2985—In depth localisation, e.g. using positron emitters; Tomographic imaging (longitudinal and transverse section imaging; apparatus for radiation diagnosis sequentially in different planes, steroscopic radiation diagnosis)
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/02—Devices for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
- A61B6/03—Computerised tomographs
- A61B6/037—Emission tomography
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/52—Devices using data or image processing specially adapted for radiation diagnosis
- A61B6/5258—Devices using data or image processing specially adapted for radiation diagnosis involving detection or reduction of artifacts or noise
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/161—Applications in the field of nuclear medicine, e.g. in vivo counting
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/20—Measuring radiation intensity with scintillation detectors
- G01T1/202—Measuring radiation intensity with scintillation detectors the detector being a crystal
Abstract
A PET device is provided with a plurality of detectors having detector signal processing sections and a data processing circuit for acquiring gamma ray generation positions. The detector signal processing unit includes a Compton cone estimating unit that estimates, as first and second Compton cones, an incidence direction of gamma rays detected by a pair of detectors. The data processing unit is provided with: the gamma ray generation device includes a coincidence count acquisition unit that acquires coincidence count information of gamma rays, a scattering surface estimation unit that estimates a scattering surface of gamma rays, a first intersection determination unit that determines whether or not a first intersection is present at which surfaces of first and second Compton cones overlap each other, a second intersection determination unit that determines whether or not a second intersection is present at which the first intersection and the scattering surface overlap each other, and a gamma ray generation position acquisition unit that acquires a gamma ray generation position from TOF information of the scattered coincidence count measurement lines and gamma rays.
Description
Technical Field
The present invention relates to a PET apparatus and a method for acquiring a gamma ray generation position corresponding to a scatter coincidence count in the PET apparatus.
Background
For the observation of biological functions, the diagnosis of malignant tumors, and the like, PET devices that perform positron emission tomography (PET: positron Emission Tomography) can be used. A nuclear medicine imaging device disclosed in patent No. 4588042 discloses a method of estimating a gamma ray generation site (gamma ray generation position) by estimating an incidence direction of a gamma ray by compton scattering kinematics, based on determination of coincidence count of annihilation gamma rays (pair annihilation gamma-ray, hereinafter simply referred to as "gamma rays"). In patent No. 4588042, the accidental coincidence count and the scattered coincidence count are removed as noise by estimating the gamma ray generation position.
Further, a PET apparatus shown in non-patent literature (Hamidreza Hemmati, et al, "Compton scatter tomography in TOF-PET," phys.med.biol.62 7641 (2017)) discloses a method of estimating a scattering surface and a gamma ray incidence direction based on energy information obtained by a detector and information matching a count. In the non-patent document, the gamma ray generation position is estimated based on the estimation and TOF (Time Of Flight) information. The gamma ray generation position in the non-patent document 1 is estimated from a plurality of candidates that have a ring shape by calculation of monte carlo simulation (Monte Carlo simulation).
As described above, in japanese patent No. 4588042, only the accidental coincidence count and the scattered coincidence count are removed as noise. In contrast, in the above-mentioned non-patent document, it is intended that the actual sensitivity is improved by estimating the gamma ray generation position at which the scattering matches the count. Thereby, realization of high-definition image capturing is intended. However, in the case of estimating the gamma-ray generation position from a plurality of candidates with high accuracy by the method shown in the above-mentioned non-patent document, a long calculation time is required.
Disclosure of Invention
In view of the above-described problems, an object of the present invention is to provide a PET apparatus capable of performing high-definition image capturing in a short time and a method for acquiring a gamma ray generation position by which scatter in the PET apparatus matches a count.
One aspect of the present invention provides a method for acquiring a gamma ray generation position corresponding to a scatter coincidence count in a PET apparatus, the method including: a step of detecting gamma rays by a pair of detectors arranged around and sandwiching an object; estimating the incident direction of the gamma rays detected by the pair of detectors as first and second Compton cones; acquiring coincidence count information of gamma rays detected by a pair of detectors; estimating a scattering surface of the gamma ray based on the coincidence count measurement line based on the coincidence count information and the energy information of the gamma ray; determining whether a first intersection line where the surfaces of the first and second Compton cones overlap each other exists; determining whether or not there is a second intersection point at which the first intersection line and the scattering surface overlap, when there is a first intersection line and neither of the first and second compton cones overlap with the measurement line that matches the count; and if the second intersection point exists, calculating a measurement line of the scattered coincidence count according to the second intersection point, and acquiring a gamma ray generation position according to the measurement line of the scattered coincidence count and TOF information of the gamma ray.
According to this PET apparatus acquisition method, when the second intersection exists, the scatter coincidence count can be used as data for acquiring the gamma ray generation position. This substantially improves the sensitivity of the detector compared to the case where all of the scatter coincidence counts are removed only as noise. For example, when there is 1 point at the second intersection, calculation such as monte carlo simulation, which adds complex conditions such as the shape of the subject and the line source distribution, is not necessary, and the gamma ray generation position can be estimated using the information of the scatter coincidence count that is directly measured. Therefore, according to the above-described acquisition method, high-definition image capturing can be performed in a short time.
When the first intersection line is present and the first intersection line and the coincidence count measurement line overlap, the gamma ray generation position may be obtained from the TOF information and the coincidence count measurement line. In this case, the true coincidence count can be clearly selected, and therefore, higher-definition image capturing can be performed.
If it is determined that the first intersection does not exist, the following steps may not be performed: judging whether the second intersection point exists or not; calculating a measurement line of the scattering coincidence count; and a step of acquiring the gamma ray generation position. In this case, since unnecessary accidental coincidence counts can be removed as noise, high-definition image capturing can be performed.
If it is determined that the second intersection point does not exist, the following steps may not be performed: calculating a measurement line of the scattering coincidence count; and a step of acquiring the gamma ray generation position. In this case, since the unnecessary scatter coincidence count can be removed as noise, high-definition image capturing can be performed.
Another aspect of the present invention provides a PET apparatus including: a plurality of detectors which are arranged around the subject and have signal processing sections; a data processing unit that obtains a gamma ray generation position based on information detected by a plurality of detectors, the signal processing unit including a compton cone estimating unit that estimates, as first and second compton cones, an incidence direction of gamma rays respectively incident on a pair of detectors sandwiching an object among the plurality of detectors, the data processing unit including: a coincidence count acquisition unit that acquires coincidence count information of gamma rays detected by a pair of detectors; a scattering surface estimating unit for estimating a scattering surface of the gamma ray based on the coincidence count measurement line based on the coincidence count information and the energy information of the gamma ray; a first intersection determination unit that determines whether or not there is a first intersection in which the surfaces of the first and second Compton cones overlap each other; a second intersection determination unit that determines whether or not there is a second intersection at which the first intersection and the scattering surface overlap, when there is a first intersection and neither of the first and second compton cones overlap with the measurement line that matches the count; a coincidence count line calculation unit that calculates a measurement line of the scatter coincidence count from the second intersection point when the second intersection point exists; and a gamma ray generation position acquisition unit that acquires a gamma ray generation position from the scattered coincidence count measurement line and the gamma ray TOF information.
According to this PET apparatus, the gamma ray generation position acquisition unit can use the scatter coincidence count as data for acquiring the gamma ray generation position when the second intersection determination unit determines that the second intersection exists. This substantially improves the sensitivity of the detector compared to the case where all of the scatter coincidence counts are removed only as noise. In addition, for example, when it is determined that 1 point exists at the second intersection, the gamma-ray generation position obtaining unit can estimate the gamma-ray generation position using information of the scatter coincidence count without adding calculation such as monte carlo simulation in which complicated conditions such as the shape of the subject and the line source distribution are added. Therefore, according to the PET apparatus, high-definition image capturing can be performed in a short time.
Each of the plurality of detectors may have a plurality of gamma ray detection sections stacked in the incidence direction of the gamma rays, and each of the plurality of gamma ray detection sections may have a scintillator and a photosensor array. In this case, the detection performance such as the position resolution and the time resolution of the gamma ray of each detector can be improved.
The thickness of the scintillator included in the gamma ray detection section may be thinner as the scintillator is closer to the subject. In this case, not only the high time resolution performance but also the resolution of the compton cone estimated by the compton cone estimating section can be improved.
The scintillators can each also be composed of the same material, which can include LSO: ce crystal or LYSO: and (5) crystallizing Ce. In this case, the manufacturing cost is reduced, and the sensitivity of gamma rays in the scintillator can be improved.
The Compton scattering ratio of the scintillator located on the side close to the gamma ray generation position may also be higher than that of the scintillator located on the side far from the gamma ray generation position. In addition, the scintillator positioned near the side of the gamma ray generation site may also contain LaBr 3 : ce crystals, a scintillator located on the side remote from the gamma ray generation site contains LSO: ce crystal or LYSO: and (5) crystallizing Ce. In this case, the light is emitted by the scintillator located on the side close to the gamma ray generation positionThe Compton scattering ratio is improved and the sensitivity of gamma rays in a scintillator located on the side away from the gamma ray generation position can be improved.
The thickness of the scintillator may be 2mm or more and 5mm or less. In this case, a sufficient coincidence count timing resolution can be obtained. In addition, the sensitivity of gamma rays can be ensured and the compton cone can be well estimated.
Drawings
Fig. 1A is a schematic view of a PET apparatus according to the present embodiment, and fig. 1B is a schematic view of a detector ring of the PET apparatus;
Fig. 2 is a block diagram of a radiation position detector and a detector signal processing section;
FIG. 3 is a block diagram showing a data processing section;
FIG. 4 is a schematic diagram for explaining a method of acquiring a scattering coincidence count gamma ray generation position;
FIG. 5 is a cross-sectional view along the α - α ray of FIG. 4;
FIG. 6 is a flow chart of a method of acquiring scattered coincidence count gamma ray generation locations;
fig. 7 is a flowchart showing a specific example of step S1 shown in fig. 6.
Detailed Description
Hereinafter, a preferred embodiment of one aspect of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same elements or elements having the same functions are denoted by the same reference numerals, and overlapping descriptions are omitted.
Fig. 1A is a schematic view of the PET apparatus of the present embodiment. Fig. 1B is a schematic view of a detector ring of the PET apparatus. The PET apparatus 1 shown in fig. 1A is an apparatus that detects radiation emitted from a subject (object) T. The subject T is, for example, a living organism or an object to which an agent identified by a positron-emitting nuclide (positron-emitting radioisotope) is administered. According to the PET apparatus 1, tomographic images of the subject T can be acquired at a plurality of cutting positions based on the detected radiation.
The PET apparatus 1 includes: a bed (not shown) on which the subject T is placed, a bridge 2 having an opening with a circular cross section, a data processing unit 3 for transmitting data detected by a detector ring in the bridge 2, and an image processing unit 4 for reconstructing an image based on the data processed by the data processing unit 3. As shown in fig. 1B, a plurality of radiation position detectors (detectors) 10 are annularly arranged on a circumference around a predetermined line L0 as a center line in a detector ring in the bridge 2 of the PET apparatus 1. In the detector ring, adjacent radiation position detectors 10 are in contact with each other. When gamma rays emitted from the subject T are detected by the PET apparatus 1, the subject T is positioned in the opening of the bridge 2. At this time, the plurality of radiation position detectors 10 are arranged around the subject T.
Fig. 2 is a block diagram of the radiation position detector and the detector signal processing section. The radiation position detector 10 shown in fig. 2 is a sensor for acquiring the incidence position, incidence energy, incidence time, and incidence direction of an incident gamma ray. The radiation position detector 10 includes: the gamma ray detection units 11 to 14 using DOI (depth of action, depth Of Interaction) technology, and a detector signal processing unit (signal processing unit) SP that processes signals transmitted from the gamma ray detection units 11 to 14. The gamma ray detection units 11 to 14 are devices that detect incident gamma rays and generate electric signals, and are stacked on each other in the incident direction of the gamma rays. The gamma ray detection unit 11 is disposed at a position closest to the subject T, and the gamma ray detection unit 14 is disposed at a position farthest from the subject T. In fig. 2, the gamma ray detecting sections 11 to 14 are shown as side views, and the detector signal processing section SP is shown as a block diagram. In the following, the direction in which the gamma ray detection sections 11 to 14 are stacked on each other is referred to as "stacking direction" or "incidence direction of gamma rays".
The gamma ray detection unit 11 includes a scintillator 21a, a photosensor array 22a, and a printed circuit board 23a.
The scintillator 21a is a member that generates scintillation light by absorption of gamma rays, and includes a plurality of scintillator portions (not shown) two-dimensionally arranged along a direction orthogonal to the stacking direction. The plurality of scintillator portions are arranged in a matrix, for example. The scintillator portions may be physically separated from each other, or may be laser-processedThe treatments are optically separated from each other. In the case where the scintillator portions are physically separated from each other, a light shielding layer may be provided between adjacent scintillator portions. The thickness of the scintillator 21a is, for example, 2mm or more from the viewpoint of ensuring the sensitivity of gamma rays and well estimating compton cone. Further, from the viewpoint of obtaining a sufficient coincidence count timing resolution (CTR: coincidence Timing Resolution), the thickness of the scintillator 21a is, for example, 5mm or less. The CTR is sufficiently set to, for example, 100ps or less. The material constituting the scintillator 21a is, for example, LSO: ce crystallization, LYSO: ce crystals, or LaBr 3 : ce crystals, and the like. From the standpoint of cost and gamma ray sensitivity, the scintillator 21a may also utilize LSO: ce crystal or LYSO: ce crystal. From the standpoint of good CTR and Compton scattering ratios, the scintillator 21a may be composed of LaBr 3 : ce crystal.
The photosensor array 22a is a member for detecting scintillation light generated by the scintillator 21a, and includes a plurality of photosensors (not shown) two-dimensionally arranged along a direction orthogonal to the stacking direction. Each photosensor is provided corresponding to each scintillator portion of the scintillator 21 a. In this embodiment, the photosensor array 22a is an MPPC (Multi-pixel photon counter ). The pitch of the sensors is, for example, about 1mm or more and about 4mm or less.
The printed circuit board 23a is a member that processes light detected by the photosensor array 22a as an electrical signal. The printed circuit board 23a includes, for example, an amplifier circuit, a converter, and the like. The electrical signal processed by the printed circuit board 23a is transmitted to the detector signal processing unit SP via the wiring W1. The printed circuit board 23a sums the outputs from the cathodes of the respective photosensors, and is configured to pick up a digital signal (timing pickup signal) of the timing thereof, and to send the timing pickup signal to the detector signal processing section SP. The printed circuit board 23a converts the output from the anode of each photosensor into 4 output analog signals (4 ch analog signals) that can be subjected to center of gravity calculation, and sends the 4ch analog signals to the detector signal processing unit SP. The wiring W1 is, for example, a Flexible Flat Cable (FFC).
The gamma ray detection units 12 to 14 have corresponding scintillators 21b to 21d, corresponding photosensor arrays 22b to 22d, and corresponding printed circuit boards 23b to 23d, as in the gamma ray detection unit 11. The scintillators 21b to 21d have the same structure as the scintillator 21 a. The photosensor arrays 22b to 22d have the same structure as the photosensor array 22 a. The printed circuit boards 23b to 23d have the same configuration as the printed circuit board 23a, and are connected to the detector signal processing section SP via corresponding wirings W2 to W4.
The thickness of the scintillators 21a to 21d in the gamma ray detection units 11 to 14 may be the same as each other or may be different from each other. Alternatively, a part of the thickness of the scintillators 21a to 21d may be different from other ones. In the case where the thickness of the scintillators 21a to 21d is different from each other, the scintillator may be thinner as the scintillator approaches the subject T. That is, in the gamma ray detecting sections 11 to 14, the thickness of the scintillator 21a is the thinnest, and the thickness of the scintillator 21d is the thickest. In the case where the thickness of the scintillator is thin, good TOF information can be obtained. In addition, the sensitivity and time resolution performance of the radiation position detector 10 can be adjusted according to the specification of the PET apparatus 1. The thickness of the scintillators 21b to 21d may be larger than 5mm. The scintillators 21a to 21d may be formed of the same material or different materials. In addition, a part of the scintillators may be formed of a material different from that of the other scintillators. In the case where the scintillators 21a to 21d are constituted by mutually identical materials, for example, LSO may be used as the materials: ce crystal or LYSO: ce crystal. In the case where the materials constituting the scintillators 21a to 21d are different from each other, or in the case where a part of the scintillators are made of a material different from other scintillators, for example, the compton scattering ratio of the scintillator located on the side close to the gamma ray generation position (for example, the prescribed portion of the subject T) may be higher than the compton scattering ratio of the scintillator located on the side away from the gamma ray generation position. Specifically, the scintillator located near the gamma ray generation position may be composed of LaBr 3 : ce crystal, a scintillator located on the side away from the gamma ray generation site may also be composed of LSO: ce crystal or LYSO: ce crystal. In this case, the use of a seat restThe scintillator on the side near the gamma ray generation position can increase the compton scattering ratio, and the sensitivity of gamma rays in the scintillator on the side far from the gamma ray generation position can be increased. In the present embodiment, the scintillators located on the side closer to the gamma ray generation position are the scintillators 21a, 21b, and the scintillators located on the side farther from the gamma ray generation position are the scintillators 21c, 21d, but the present invention is not limited thereto. The scintillator located on the side close to the gamma ray generation position may be only the scintillator 21a, and the scintillator located on the side far from the gamma ray generation position may be only the scintillator 21d.
The detector signal processing unit SP is a signal processing circuit that obtains (calculates) gamma ray incidence position information, gamma ray incidence energy information, gamma ray incidence time information, and gamma ray incidence angle information from the signals generated by the gamma ray detection units 11 to 14. The functional configuration of the detector signal processing unit SP of fig. 2 will be described below. The detector signal processing unit SP shown in fig. 2 includes: an incidence position acquisition unit SP1, an energy acquisition unit SP2, an incidence time acquisition unit SP3, and a compton cone estimation unit SP4.
The incidence position acquisition unit SP1 acquires incidence position information of gamma rays incident on the radiation position detector 10. The incidence position acquisition unit SP1 acquires incidence position information of gamma rays from each of the gamma ray detection units 11 to 14. The incidence position acquisition unit SP1 converts, for example, the 4ch analog signals received from the printed circuit boards 23a to 23d into digital signals, and performs center of gravity position calculation using the digital signals. Thus, the incidence position acquisition unit SP1 acquires incidence position information of the gamma rays incident on the gamma ray detection units 11 to 14, respectively. The incidence position information corresponds to, for example, position information of the scintillator block detected by the scintillators 21a to 21 d.
The energy acquisition unit SP2 acquires energy information of gamma rays incident on the radiation position detector 10. The energy acquisition unit SP2 acquires energy information of gamma rays from each of the gamma ray detection units 11 to 14. At this time, the energy acquisition unit SP2 performs correction for matching the relative values of the energies acquired by the gamma ray detection units 11 to 14. The energy obtaining unit SP2 converts, for example, 4ch analog signals received from the printed circuit boards 23a to 23d into digital signals, and obtains the sum of the digital signals, thereby obtaining energy information of gamma rays.
The incidence time acquisition unit SP3 acquires incidence time information of gamma rays incident on the radiation position detector 10. The incidence time acquisition unit SP3 acquires incidence time information of gamma rays from each of the gamma ray detection units 11 to 14. At this time, the incident time acquisition unit SP3 performs correction of the delay time corresponding to the difference in position of each gamma ray detection unit 11 to 14, the difference in thickness of the scintillators 21a to 21d, the difference in length of the wirings W1 to W4, and the like. The incidence Time acquisition unit SP3 converts the timing pickup signals received from the printed circuit boards 23a to 23d into incidence Time data of gamma rays using, for example, a TDC (Time-to-Digital Converter) circuit.
The compton cone estimating unit SP4 estimates the incident direction of the gamma ray incident on each radiation position detector 10 as a compton cone. The compton cone estimating unit SP4 estimates a cone surface having an angle (scattering angle), i.e., compton cone, of the incident gamma ray to the radiation position detector 10 based on information of energy applied to electrons by compton scattering, energy of scattered gamma rays, a site where compton scattering occurs, and a site where scattered gamma rays are photoelectrically absorbed. The angular resolution of the estimated compton cone is, for example, 5 degrees or less.
Compton cones are regions that represent the direction in which 1 photon of a gamma ray flies. Compton scattering of photons is a phenomenon that causes elastic scattering of photons and electrons. Forward scattering (forward scattering) dominates at high energies of the photons (e.g., at 511keV energy of the photons). Therefore, in the present embodiment, the location where compton scattering occurs in the detector closest to the subject T among the detectors that detect gamma rays is set to FIP (First Interaction Point), and the compton cone is estimated using the FIP. FIP can also be calculated from the recoil electrons (recoil electrons) in compton scattering and the energy of the scattered gamma rays versus the scattering angle.
The data processing unit 3 is a signal processing circuit that obtains (calculates) gamma ray generation site information (gamma ray generation site) in the subject T based on the signal generated by the radiation position detector 10. The data processing unit 3 is an electronic control unit having, for example, a CPU (central processing unit ), a ROM (Read Only Memory), a RAM (random access Memory), and the like. In the data processing unit 3, for example, a program stored in a ROM is loaded in a RAM, and the CPU executes the program loaded in the RAM, thereby realizing various functions.
Next, the functional configuration of the data processing unit 3 will be described with reference to fig. 3. Fig. 3 is a block diagram showing a data processing section. The data processing unit 3 shown in fig. 3 includes: the coincidence count obtaining unit 31, the scattering surface estimating unit 32, the first intersection determining unit 33, the second intersection determining unit 34, the coincidence count line calculating unit 35, and the gamma ray generating position obtaining unit 36.
The coincidence count acquisition unit 31 acquires coincidence count information of gamma rays detected by each radiation position detector 10. The coincidence count information is information indicating a phenomenon (event) in which the two radiation position detectors 10 detect gamma rays within a prescribed time range. Accordingly, the coincidence count acquiring unit 31 first determines whether each of the radiation position detectors 10 detects gamma rays simultaneously or within a predetermined time range based on the electric signals transmitted from each of the radiation position detectors 10. When the above determination is positive, the gamma ray information transmitted from each radiation position detector 10 is acquired. Then, the coincidence count obtaining unit 31 calculates a coincidence count measurement line LOR1 (see fig. 4 described later) based on the obtained coincidence count gamma ray information. In addition, the prescribed time range is, for example, 8×10 -9 Within seconds.
The scattering surface estimating unit 32 estimates a scattering surface of gamma rays based on the measurement line of the coincidence count calculated based on the coincidence count information and the energy information of the gamma rays incident on the radiation position detector 10. The scattering surface estimating unit 32 is based on, for example, energy information of gamma rays obtained by a pair of radiation position detectors 10 sandwiching the subject T and a coincidence meterThe number of measurement lines LOR1, and the scattering surface SS of the gamma ray are estimated (see fig. 4 described later). Specifically, the scattering surface estimating unit 32 first calculates the scattering angle θab from the energy Ea obtained from one radiation position detector 10 that detects the unscattered gamma rays and the energy Eb obtained from the other radiation position detector 10 that detects the gamma rays scattered once at an arbitrary position (scattering position). Then, all positions at which the scattering angle θab is established are plotted along the detection positions of the pair of radiation position detectors 10, whereby the scattering surface SS, which is the surface of the oblong body, is estimated. The scattering surface SS corresponds to the portion indicated by a broken line in fig. 4. The scattering angle θab is defined by "θab=cos -1 (2-Ea/Eb) ". The energy Ea corresponds to 511keV as the stationary mass energy of the electrons. The energy Eb is greater than 1/3 of the energy Ea and the specific energy Ea is smaller.
The first intersection determination unit 33 determines whether or not an intersection (first intersection) where the surfaces of the estimated compton cones overlap each other is present. The first intersection determination unit 33 determines whether or not there is a first intersection CL1 (see fig. 4 described below) in which the surfaces of the first compton cone CCA and the second compton cone CCB (see fig. 4 described below) overlap with each other, for example, estimated by the pair of radiation position detectors 10 sandwiching the subject T. The first intersecting line may have a line shape or a dot shape. In addition, when either the first intersection line or the first and second compton cones CCA, CCB coincide with a measurement line of coincidence count, the coincidence count line is set to an unscattered true coincidence count line. In this case, the gamma ray generation position is obtained from the measurement line and the TOF information.
The second intersection determination unit 34 determines whether or not a second intersection is present at which the first intersection and the scattering surface overlap, when the first intersection exists and neither of the compton cones overlaps with the measurement line that matches the count. The second intersection determination unit 34 determines whether or not there is a second intersection CP2 (see fig. 4 described later) at which the first intersection CL1 and the scattering surface SS overlap, for example, when the first intersection CL1 exists and neither of the first nor second compton cones CCA and CCB overlaps the measurement line LOR1 corresponding to the count. The second intersection point is estimated as a compton scattering point. The second intersection determination unit 34 does not determine whether or not the second intersection exists if the first intersection does not exist. In this case, the data processing section 3 determines the gamma rays detected by the pair of radiation position detectors 10 as accidental coincidence counts. Alternatively, the second intersection determination unit 34 does not determine whether or not the second intersection exists when at least one of the first and second compton cones CCA and CCB coincides with the measurement line LOR1 corresponding to the count. In this case, the coincidence count acquired by the coincidence count acquisition unit 31 is set to be a true coincidence count. In the present embodiment, at least one of the first and second compton cones CCA and CCB overlaps with the measurement line LOR1, and the whole of the measurement line LOR1 may overlap with at least one of the first and second compton cones CCA and CCB.
When it is determined that the second intersection exists, the coincidence count line calculation unit 35 calculates a measurement line of the scattered coincidence count from the second intersection. For example, when the second intersection CP2 is present, the coincidence count line calculation unit 35 calculates a measurement line LOR2 (see fig. 4 described later) of the scatter coincidence count based on the second intersection CP 2. The measurement line LOR2 corresponds to, for example, a straight line connecting the radiation position detector 10 and the second intersection point. In the case where the second intersection point does not exist, the coincidence count line calculation portion 35 does not calculate a measurement line of the scattered coincidence count. In this case, the data processing unit 3 processes the scatter coincidence count as noise. When it is determined that there are multiple second intersections, the coincidence count line calculation unit 35 calculates a measurement line of the scattered coincidence count for each of the second intersections.
The gamma ray generation position acquisition unit 36 acquires the gamma ray generation position of the scattered coincidence count from the measurement line of the scattered coincidence count and the TOF information of the gamma ray. The gamma ray generation position obtaining unit 36 obtains a gamma ray generation position AP (see fig. 4 described later) from, for example, the calculated scattered coincidence count measurement line LOR2 and the TOF information of the gamma rays. In addition, for example, when the first intersection CL1 exists and at least one of the first and second compton cones CCA and CCB overlaps with the line of measurement LOR1 corresponding to the count, the gamma ray generation position obtaining unit 36 obtains the gamma ray generation position based on the line of measurement LOR1 corresponding to the count and the TOF information. When it is determined that the second intersection is not present, the gamma-ray generation position acquisition unit 36 acquires the gamma-ray generation position without using the scatter coincidence count. In this case, the data processing unit 3 also processes the scatter coincidence count as noise. When it is determined that there are multiple second intersections, the gamma ray generation position obtaining unit 36 estimates the gamma ray generation position by, for example, monte carlo simulation using the measurement lines of the scatter coincidence count of the respective second intersections and the TOF information.
Next, an example of a method for acquiring a gamma ray generation position by using the scatter coincidence count of the PET apparatus 1 of the present embodiment will be described with reference to fig. 4 to 6. Fig. 4 is a schematic diagram for explaining a method of acquiring a gamma ray generation position of a scatter coincidence count. Fig. 5 is a cross-sectional view along the alpha-alpha ray of fig. 4. FIG. 6 is a flow chart of a method of acquiring a scattered coincidence count gamma ray generation location. Next, as shown in fig. 4, a method of acquiring a gamma ray generation position corresponding to a scatter coincidence count in the case of using a pair of radiation position detectors 10A and 10B will be described. The radiation position detectors 10A and 10B shown in fig. 4 are not arranged in point symmetry with respect to a predetermined line L0 (see fig. 1B) and are arranged so as to sandwich the subject T. In fig. 4, the radiation position detectors other than the radiation position detectors 10A, 10B are omitted.
As shown in fig. 4 to 6, the incidence position, incidence energy, and incidence time of the gamma ray incident on each of the radiation position detectors 10A and 10B are acquired, and the incidence direction of the gamma ray is estimated as the first and second compton cones CCA and CCB (step S1). In step S1, first, gamma rays incident on the radiation position detectors 10A and 10B are detected, and electric signals (for example, 4ch analog signals, timing pickup signals, and the like) are generated. Next, the incident position acquiring unit SP1, the energy acquiring unit SP2, and the incident time acquiring unit SP3 acquire information indicating the incident position, the incident energy, and the incident time of the gamma ray incident on each of the radiation position detectors 10A and 10B from the electric signals. Next, the compton cone estimating unit SP4 estimates the incident direction of the gamma ray as the first compton cone CCA and the second compton cone CCB from the energy and the incident position of the acquired gamma ray.
The above step S1 will be described in detail with reference to fig. 7. Fig. 7 is a flowchart showing a specific example of step S1 shown in fig. 6. As shown in fig. 7, first, gamma rays are incident on the radiation position detector 10A (step S101). Next, the gamma ray detection units 11 to 14 included in the radiation position detector 10A detect the incidence position, incidence energy, and incidence time of the incident gamma ray (steps S102a to S102 d). Next, the incident energy and the incident time of the gamma ray detected by each of the gamma ray detection units 11 to 14 are corrected (steps S103a to S103 d). Next, the detector signal processing unit SP determines whether or not the incident time of each of the gamma ray detecting units 11 to 14 matches (step S104). The "time of incidence coincidence" in step S104 may not be limited to the complete coincidence. For example, 1X 10 may also be present -10 Time range of the second degree.
Next, when it is determined that the respective incident timings match (YES in step S104), a first compton cone CCA is calculated using the signals generated in the gamma ray detection units 11 to 14 (step S105). The events determined to be coincident at the respective incident times are compton scattering across the gamma ray detectors 11 to 14, and two events are acquired, for example. In step S105, the sum of the energies is calculated from the energy information of each event determined in step S104. The compton cone estimator SP4 calculates FIP (first interaction point ) from the incident position information and the energy information of the gamma rays received from the gamma ray detectors 11 to 14. Based on the calculated FIP and information of the place where the scattered gamma ray is photoelectrically absorbed, the result of estimation of the incidence direction of the gamma ray incident on the radiation position detector 10A is calculated as the first compton cone CCA.
Next, it is determined whether or not the energy acquired by the radiation position detector 10A is valid (step S106). In step S106, it is determined whether the calculated sum of the energies is valid or not based on the energy window. Next, the FIP, the energy sum information, the incident time information, the estimated information of the first compton cone CCA and the like are converted into digital data (step S107). In step S107, the information is sent to, for example, a buffer and a serial data conversion circuit. Then, the converted data is transmitted to and recorded in the data processing section 3 (step S108).
On the other hand, when it is determined that the respective incident times do not match (step S104: NO), step S106 is performed without performing step S105. At this time, in step S106, the energy acquired from each of the gamma ray detectors 11 to 14 is determined to be valid based on the energy window. The event determined to be non-coincident is, for example, an event of photoelectric absorption performed by any one of the gamma ray detection units 11 to 14. When it is determined in step S106 that the energy is effective, steps S107 and S108 are performed. Thus, the data of the effective energy is transmitted together with the incident position information and the incident time information and recorded in the data processing unit 3.
In the radiation position detector 10B, the FIP calculated along the flowchart shown in fig. 7, the incident position information, the sum of energies, the incident time information, the estimated second compton cone CCB, and other information are also recorded as data.
Returning to fig. 4 to 6, after step S1, coincidence count information of the gamma rays detected by the radiation position detectors 10A and 10B is acquired (step S2). In step S2, the coincidence count obtaining unit 31 determines whether or not the coincidence count is formed by the gamma ray detection by the radiation position detectors 10A and 10B, based on the electric signals transmitted from the radiation position detectors 10A and 10B. When the coincidence count information is acquired, a line LOR1 for coincidence count is calculated based on the coincidence count information. Further, TOF information of gamma rays, which is a difference between the incident timings of the radiation position detectors 10A and 10B, is acquired. When coincidence count information is not acquired, the gamma rays detected by the radiation position detectors 10A and 10B are determined not to be radiation generated from the same gamma ray generation position. In this case, steps S3 to S9 described below may not be performed.
Next, the presence or absence of the first and second compton cones CCA, CCB is determined on the information of the radiation position detectors 10A, 10B for which the coincidence count is acquired (step S3). If there are the first and second compton cones CCA and CCB (YES in step S3), step S4 described later is performed. If at least one of the first and second compton cones CCA and CCB is not present (step S3: NO), the gamma rays incident on the radiation position detectors 10A and 10B are determined to include coincidence counts including coincidence counts of coincidence and scatter, which are also acquired in a normal PET apparatus (step E1). In this case, since the identification of the accidental coincidence count and the scattered coincidence count is not performed and the steps S4 to S9 described later are not performed.
Next, the scattering surface SS of the gamma ray is estimated from the energies acquired by the measurement line LOR1 and the radiation position detectors 10A and 10B corresponding to the count (step S4). In step S4, the scatter angle is calculated from the energy acquired from the radiation position detector 10A and the energy acquired from the radiation position detector 10B. Then, all the positions where the scattering angles are established are plotted along the incident positions in the radiation position detectors 10A, 10B, whereby the scattering surface SS (corresponding to the portion indicated by the broken line in fig. 4) as the surface of the elongated ellipsoid is estimated.
Unlike step S4 described above, the presence or absence of the first intersection line CL1 at which the surfaces of the estimated first compton cone CCA and second compton cone CCB overlap with each other is determined (step S5). When it is determined in step S5 that the first intersecting line CL1 exists (YES in step S5), step S6 described later is performed. On the other hand, when it is determined in step S5 that the first intersection CL1 is not present (step S5: NO), the gamma rays incident on the radiation position detectors 10A, 10B are determined to be accidentally counted (step E2). In this case, since the acquisition of the gamma ray generation position is not completed, steps S6 to S9 described later are not performed. Steps S4 and S5 may be performed at the same time or at different times. For example, step S4 may be performed after step S5 is performed.
Next, it is determined whether or not at least one of the first compton cone CCA and the second compton cone CCB coincides with the measurement line LOR1 that matches the count (step S6). When it is determined that at least one of the first compton cone CCA and the second compton cone CCB coincides with the line of measurement LOR1 of the coincidence count (YES in step S6), the coincidence count calculated in step S2 is acquired as a true coincidence count (step E3). After step E3, the gamma-ray generation position obtaining unit 36 obtains the gamma-ray generation position from the TOF information of the radiation position detectors 10A and 10B and the measurement line LOR1 corresponding to the count. Therefore, steps S7 to S9 described later are not performed.
When neither the first compton cone CCA nor the second compton cone CCB overlaps with the measurement line LOR1 that matches the count (step S6: NO), the presence or absence of the second intersection CP2 at which the first intersection CL1 overlaps with the scattering surface SS is determined (step S7). When it is determined that the second intersection CP2 is not present (step S7: NO), it is determined that any one of the gamma rays is subjected to multiple scattering. In this case, the data processing unit 3 determines the scatter coincidence count as noise (step E4), and does not perform steps S8 and S9 described later. Further, if there are many events in which gamma rays scatter multiple times within the subject and reach the radiation position detector 10, the energy of incident gamma rays becomes low due to the multiple scattering. The incident gamma rays having lower energy are invalidated in the energy window determination (step S106 described above). The proportion of events in which the gamma rays scatter multiple times and reach the radiation position detector 10 is lower than events in which the gamma rays scatter once and reach the radiation position detector 10. Therefore, the proportion of the image in which the second intersection CP2 is determined to be absent in step S7 is also low. Therefore, steps S1 to S9 including steps S8 and S9 described later are useful as a method for estimating the gamma-ray generation position AP.
When it is determined that the second intersection CP2 exists (YES in step S7), the second intersection CP2 is determined as a position (scattering position) where one of the gamma rays is scattered (step S8). In step S8, it is determined that either of the gamma rays is scattered only once. The coincidence count line calculation unit 35 calculates the line LOR2 for measuring the scatter coincidence count from the second intersection point CP 2.
Next, the gamma ray generation position AP of the scattered coincidence count is obtained from the TOF information of the measurement line LOR2 of the scattered coincidence count and the gamma ray (step S9). In step S9, the gamma ray generation position obtaining unit 36 obtains the gamma ray generation position AP from the measurement line LOR2 of the scatter coincidence count and the TOF information of the gamma ray. By performing the above steps for each of the plurality of radiation position detectors 10, the image processing section 4 can form a tomographic image based on the acquired information of the gamma ray generation position. The image processing unit 4 acquires a tomographic image by performing image reconstruction based on the scatter coincidence count set to be valid in the data processing unit 3, the true coincidence count obtained in step E3, and the coincidence count including the scatter and accidental coincidence count obtained in step E1.
The operational effects of the method for acquiring the gamma ray generation position corresponding to the scatter count in the PET apparatus 1 of the present embodiment described above will be described. In the present embodiment, instead of only the first intersection line CL1 where the surfaces of the first compton cone CCA and the second compton cone CCB overlap each other, the second intersection point CP2, which is the intersection point of the scattering surface SS of the gamma ray and the first intersection line CL1, is also obtained. Then, the second intersection point CP2 is set as the compton scattering point of the gamma ray. Therefore, in the case where the second intersection point CP2 exists, the scatter coincidence count can be used as data for acquiring the line source generation position AP. This substantially improves the sensitivity of the radiation position detector 10 as compared with the case where all the scatter coincidence counts are removed only as noise. Further, the gamma-ray generation position AP can be estimated using the information of the scatter coincidence count that is directly measured without adding computation such as monte carlo simulation of complex conditions such as the shape of the subject and the line source distribution. Therefore, according to the present embodiment, high-definition image capturing can be performed in a short time.
In the present embodiment, when the first intersection line CL1 exists and the first intersection line CL1 and the line of measurement LOR1 corresponding to the count overlap, the gamma ray generation position may be obtained from the TOF information and the line of measurement LOR1 corresponding to the count.
In the present embodiment, when it is determined that the first intersection line CL1 is not present, the determination of the presence or absence of the second intersection point CP2, the calculation of the measurement line LOR2 of the scatter coincidence count, and the acquisition of the gamma ray generation position AP based on the measurement line LOR2 of the scatter coincidence count and the TOF information may not be performed. In this case, since the unnecessary occasional coincidence count and the scattering coincidence count which cannot be estimated can be removed as noise, high-definition image capturing can be performed.
In the present embodiment, when it is determined that the second intersection CP2 is not present, calculation of the measurement line LOR2 of the scatter coincidence count and acquisition of the gamma ray generation position AP based on the measurement line LOR2 of the scatter coincidence count and the TOF information may not be performed. In this case, since the unnecessary scatter coincidence count can be removed as noise, high-definition image capturing can be performed.
In the present embodiment, each of the plurality of radiation position detectors 10 may have gamma ray detection sections 11 to 14 stacked in the incidence direction of gamma rays, and each of the gamma ray detection sections 11 to 14 may have scintillators 21a to 21d and photosensor arrays 22a to 22d. In this case, the detection performance of the gamma rays in each radiation position detector 10 can be improved.
In the present embodiment, the thickness of the scintillators 21a to 21d included in the gamma ray detection units 11 to 14 may be smaller as the scintillators are closer to the subject T. In this case, the radiation position detector 10 having high time resolution performance can be realized. In addition, the resolution of the compton cone estimated by the compton cone estimating unit SP4 can be improved.
In the present embodiment, each of the scintillators 21a to 21d may be made of the same material including LSO: ce crystal or LYSO: and (5) crystallizing Ce. In this case, the manufacturing cost can be reduced, and the sensitivity of gamma rays in the scintillator can be improved.
In the present embodiment, the compton scattering ratio of the scintillator located on the side close to the gamma ray generation position may be higher than the compton scattering ratio of the scintillator located on the side far from the gamma ray generation position. In addition, the scintillator positioned near the side of the gamma ray generation site may also contain LaBr 3 : ce crystals, a scintillator located on the side remote from the gamma ray generation site contains LSO: ce crystal or LYSO: and (5) crystallizing Ce. In this case, the Compton scattering ratio is increased by using a scintillator located on the side close to the gamma ray generation position, and the bit can be increased Sensitivity of gamma rays in the scintillator on the side remote from the gamma ray generation location.
In the present embodiment, the thickness of the scintillators 21a to 21d may be 2mm or more and 5mm or less. In this case, a sufficient coincidence count timing resolution can be obtained. In addition, the sensitivity of the gamma rays can be ensured and the first and second compton cones CCA and CCB can be well estimated.
In the above, one aspect of the present invention is described in detail based on the above embodiments. However, one aspect of the present invention is not limited to the above embodiment. An aspect of the present invention may be further modified within a scope not departing from the gist thereof. For example, in the above embodiment, when the first and second compton cones overlap with each other to form a point intersection, the intersection can be estimated as a scattering point. In this case, the second intersection point may not be obtained.
In the above embodiment, the compton scattering point of the gamma ray, that is, the second intersection point is determined at one point, but the present invention is not limited thereto. There may also be several points (e.g., 2 points, etc.) at the first intersection point and the second intersection point of the scattering surface (i.e., compton scattering points). In this case, for example, a monte carlo simulation as shown in the above-mentioned non-patent document 1 in which each obtained second intersection point is a candidate may be performed, and the gamma ray generation position may be estimated. In this way, the candidates of the gamma ray generation positions are reduced to a fraction in advance, and then the monte carlo simulation can be performed. Therefore, compared with the case where only the above-described monte carlo simulation or the like is performed and the gamma-ray generation position is estimated from a plurality of candidates, the gamma-ray generation position can be estimated in a short time at a low load. Therefore, even when there are several points at the second intersection, the same operational effects as those of the above embodiment can be achieved. If there are a plurality of points at the second intersection, for example, the measurement line for the scatter coincidence count at each second intersection is calculated in step S8. Next, in step S9, the gamma ray generation position obtaining unit 36 may estimate the gamma ray generation position by, for example, monte carlo simulation using the measurement line of the scatter coincidence count at each second intersection and the TOF information.
In the above embodiment, step S4 may not be necessarily performed. For example, when step E2 is performed after step S5 and when step E3 is performed after step S6, step S4 may not be performed.
In the present embodiment, the radiation position detector includes 4 gamma ray detection sections, but is not limited thereto. The radiation position detector may have 5 or more gamma ray detection sections from the viewpoint of improving the sensitivity of gamma rays. In addition, the radiation position detector may have 3 or less gamma ray detection sections from the viewpoint of cost.
Claims (11)
1. A method for acquiring a gamma ray generation position corresponding to a scatter coincidence count in a PET device is provided with:
a step of detecting gamma rays by a pair of detectors arranged around and sandwiching an object;
estimating the incident direction of the gamma rays detected by the pair of detectors as first and second compton cones;
acquiring coincidence count information of gamma rays detected by the pair of detectors;
estimating a scattering surface of the gamma ray based on a coincidence count measurement line based on the coincidence count information and the energy information of the gamma ray;
Determining the presence or absence of a first intersection line in which the surfaces of the first and second Compton cones overlap each other;
determining whether or not a second intersection point where the first intersection line and the scattering surface overlap exists when the first intersection line exists and neither of the first and second compton cones overlaps the count-up-compliant measurement line;
and calculating a measurement line of a scattered coincidence count according to the second intersection point when the second intersection point exists, and acquiring a gamma ray generation position according to the measurement line of the scattered coincidence count and TOF information of the gamma ray.
2. The method for obtaining a gamma-ray generating position according to claim 1, wherein,
a gamma ray generation location is obtained from the TOF information and the coincidence count measurement line when the first intersection exists and at least one of the first and second compton cones coincides with the coincidence count measurement line.
3. The method for obtaining a gamma-ray generating position according to claim 1 or 2, wherein,
if it is determined that the first intersection is not present, the following steps are not performed: the step of determining whether the second intersection point exists; the step of calculating the scattered coincidence count measurement line; and the step of acquiring the gamma ray generation position.
4. The method for obtaining a gamma-ray generating position according to claim 1 or 2, wherein,
if it is determined that the second intersection point does not exist, the following steps are not performed: the step of calculating the scattered coincidence count measurement line; and the step of acquiring the gamma ray generation position.
5. A PET device is provided with:
a plurality of detectors which are arranged around the subject and have signal processing sections; and
a data processing unit for acquiring a gamma ray generation position based on information detected by the plurality of detectors,
the signal processing unit includes a Compton cone estimating unit for estimating, as first and second Compton cones, directions of incidence of gamma rays respectively incident on a pair of detectors sandwiching the subject among the plurality of detectors,
the data processing unit is provided with:
a coincidence count acquisition unit that acquires coincidence count information of gamma rays detected by the pair of detectors;
a scattering surface estimating unit that estimates a scattering surface of the gamma ray based on a measurement line of coincidence count based on the coincidence count information and energy information of the gamma ray;
a first intersection determination unit that determines whether or not there is a first intersection in which surfaces of the first and second compton cones overlap each other;
A second intersection determination unit that determines whether or not a second intersection is present at which the first intersection and the scattering surface overlap, when the first intersection exists and neither of the first and second compton cones overlaps the count-up measurement line;
a coincidence count line calculation unit that calculates a measurement line of a scatter coincidence count from the second intersection point when the second intersection point exists; and
and a gamma ray generation position acquisition unit that acquires a gamma ray generation position of the scattered coincidence count from the measurement line of the scattered coincidence count and the TOF information of the gamma ray.
6. The PET device of claim 5, wherein,
each of the plurality of detectors has a plurality of gamma ray detection sections stacked in an incident direction of the gamma ray,
the plurality of gamma ray detection sections each have a scintillator and a photosensor array.
7. The PET device of claim 6, wherein,
the thickness of the scintillator included in the gamma ray detection section is thinner as it is closer to the subject.
8. The PET device according to claim 6 or 7, wherein,
the scintillators are each composed of the same material,
The material comprises LSO: ce crystal or LYSO: and (5) crystallizing Ce.
9. The PET device according to claim 6 or 7, wherein,
the Compton scattering ratio of the scintillator located on the side close to the gamma ray generation position is higher than that of the scintillator located on the side far from the gamma ray generation position.
10. The PET device of claim 9, wherein,
the scintillator located near the side of the gamma ray generation location contains LaBr 3 : the Ce is crystallized and the crystal is prepared,
the scintillator located on a side remote from the gamma ray generation location includes LSO: ce crystal or LYSO: and (5) crystallizing Ce.
11. The PET device according to any of claims 6 to 9, wherein,
the thickness of the scintillator is 2mm or more and 5mm or less.
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